#include<iostream>
using namespace std;

//变量声明
extern int a,b;
extern int c;
extern float f;

int main(){
    //变量定义
    int a,b;
    int c;
    float f;
    
    //实际初始化
    a = 10;
    b = 20;
    c = a + b;
    cout << c << endl;

    f = 70.0 / 3.0;
    cout << f << endl;


    return 0;
}